FIG. 8 of the accompanying drawing shows the basic concept of the conventional pulling method and apparatus, which has been quoted from an unexamined Japanese Patent Publication No. 75263/1975 concerning a shaped product of a solid rod.
In the drawing, a reference numeral 1 designates reinforcing fibers which are delivered out of a plurality of bobbins; a numeral 2 refers to a vessel for impregnating the reinforcing fibers with a thermosetting resin; a numeral 3 refers to a fiber strand impregnated with the resin; a reference numeral 4 denotes a preheater for heating the fiber strand 3 (for the heating means, radio-frequency wave is used in this embodiment); reference numerals 5A and 5B represent squeezing jigs for removing surplus amount of the resin from the fiber strand 3 as well as for regularizing the whole external shape thereof; a numeral 6 refers to a hot die for curing and shaping the impregnated resin; and a numeral 7 refers to a belt-type, continuous pull-out drive mechanism for grasping the shaped product and moving the same to the rightward direction.
Explaining the method of shaping the solid rod in this embodiment, the reinforcing fibers 1 to be delivered out of the bobbins are put together and then the fiber strand is caused to pass through the resin impregnating vessel 2, thereby obtaining the fiber strand 3 impregnated with the thermosetting resin. Thereafter, this fiber-strand 3 is caused to pass through the preheater 4 to heat the same, then the surplus amount of the impregnating resin is removed by the squeezing jigs 5A and 5B during or after passage of the fiber strand through the preheater, and, at the same time, external configuration of the entire fiber strand is regularized. Following this, the resin is cured in the hot die 6 to thereby obtain a predetermined shaped product. In this case, the shaped product is grasped by the pulling mechanism 7 to obtain a pulling force in the right direction. This pulling mechanism is capable of exerting continuous pulling force by a belt-type device.
While the above-described embodiment is for obtaining the solid rod, an Unexamined Japanese Patent Publications No. 96067/1978 and No. 124/1981 disclose methods for pull-out shaping of hollow tubes, which comprises winding on and around a mandrel a fiber strand impregnated with a thermosetting resin, and thereafter subjecting the resin-impregnated fiber strand to the pull-out shaping by the mandrel. Also, an Unexamined Japanese Patent Publication No. 58467/1976 discloses a shaping method of a type, in which two units of the grasping device are alternately operated as the pulling mechanism so as to enable the shaped product to be continuously pulled out.
In addition, there has been a report made by W. B. Goldworthy et al. in "The 36th (1981) Annual Society of Plastics, Session 15-F, pages 1 to 6" concerning a shaping method which is characterized in that the shaped product and the mandrel are moved together by the pulling mechanism having two units of the grasping device, although this method uses an oven type curing means.
These conventional shaping methods as described in the preceding, however, are not able to sufficiently cope with shaping of the carbon-fiber-reinforced plastic tubes of light weight, thin thickness and long length, to be used for the constructive members of, for example, a large-scaled space structure, taking advantage of the superiority in relative strength and relative modulus of elasticity of carbon fibers as the reinforcing material. In more detail, the shaped products for such purpose are required to have their ultimate weight reduction in relation to their requisite mechanical strength, for which a strength sustaining factor, for example, of the shaped product with respect to the theoretical value by the composite material (to be represented by "ROM %" in terms of reduction in thickness to 1 mm or less and precision in shaping) has to be improved. However, these conventional shaping methods did not take this ROM % into account.
Such conventional pull-out shaping method is primarily to obtain with high efficiency a thick shaped product, in which glass fibers are used as the reinforcing material. Therefore, if and when such conventional technique is to be directly applied in the practice of the precision-shaping of a product having thin thickness of 1 mm or less, using the reinforcing fibers of high modulus of elasticity (i.e. the fibers which are brittle and easily breakable) such as carbon fibers, there would inevitably take place considerable decrease in the strength sustaining factor (ROM %) which is dependent on the state of the reinforcing fibers such as breakage and disturbance in orientation of the reinforcing fibers, uneven distribution of the fibers, etc.; a mixing ratio between the fibers and the resin; and further the uniform curing property of the resin, and so forth. As the consequence of this, the value of the strength sustaining factor, in the case of the high precision and high performance products for use in the space structure, becomes not only innegligible, but also totally inadequate for shaping the carbon-fiber-reinforced plastic tubes having a wall thickness of 0.5 mm or less.
Describing this conventional shaping method for each and every process mechanism, there is, at first, a process step, in which the reinforcing fibers are delivered out of a bobbin stock in the form of fiber strand (hereinafter simply called "roving") and then the roving is wound on and around the mandrel after its being impregnated with a thermosetting resin, or the roving is impregnated with the resin after its being wound on and around the mandrel, following which they are forwarded to the subsequent preheating step. At any rate, the reinforcing fibers, in this case, come into direct contact with each of the process mechanism or are subjected to a forced bending. On account of this, when the carbon fiber is used as the reinforcing fibers, there tend to readily occur fuzzing (cracks in the fibers) and breakage of the fibers. Moreover, such resin impregnating means is difficult to control the fiber content V.sub.f (a volume fraction between the fibers and the resin), hence it is difficult to achieve the ultimate reduction in weight of the shaped product with respect to its required mechanical strength.
In addition, since a large number of bobbins are needed at the same time for supply of the reinforcing fibers in the form of roving, it is inevitable that a material feeding section of the process mechanism becomes large in its dimension and occupying area (space). Therefore, when such material feeding section is incorporated in the production line, there take place unavoidably various problems concerning the factory control, material control, and other managerial matters.
In the subsequent preheating step, there has so far been adopted a method of subjecting the only portion of the carbon-fiber-reinforced plastic (in which the carbon fibers are impregnated with the thermosetting resin) to direct induction heating by means of a micro-wave heater using a micro-wave frequency of 2 GHz and higher, in utilization of the dielectric property of the resin. This method is, however, difficult to realize the heat control at the portion of the carbon-fiber-reinforced plastic on account of the heat discharging phenomenon toward the mandrel having a large heat capacity, which not only invites disturbances in the orientation of the fibers and their maldistribution during the subsequent curing and shaping step, owing to non-uniformity in the viscosity of the molten resin prior to the curing, but also is associated with non-uniformity in the curing speed of the resin, all these phenomena constituting the factors to hinder shaping of the high performance carbon-fiber-reinforced plastic.
In the conventional curing and shaping step, a large amount of surplus thermosetting resin has to be removed, since this conventional method is primarily directed to obtain thick shaped product in the main. For removal of such excess amount of resin, various measures were taken such that the squeezing angle in the squeezing section of the hot die for the curing and shaping process is made large, or multi-stage squeezing is carried out, which tends to cause the carbon fibers to be readily broken. Also, in order to restrain back tension at the squeezing section, the speed and the temperature at the pulling operation are so established that the thermosetting resin may be gelled at the latter half part of the hot die. This tends to readily cause disturbance in the orientation of the fibers due to the moving distance of the resin in its molten and flowing state being elongated, thus causing decrease in the strength sustaining ratio (ROM %).
Mentioning about the pull-out drive system, as a recent practical construction, there is a system of moving the shaped product together with the mandrel by use of the two units of grasping mechanism. In this case, however, no sufficient consideration is given to the material for the grasping surface of the mechanism, on account of which the shaped product at its high temperature condition immediately after its passage through the hot die is gripped by a low temperature grasping surface having a large heat capacity with the consequence that the shaped product tends to be readily broken by heat shock due to quenching and be deformed by heat distortion. Further, since the alternate grasping of the shaped product by the two units of the grasping mechanism is effected by the position detection system of the grasping section, there would inevitably exist a state of instantaneous stoppage of the grasping mechanism at the time of changing the grasping operation from one mechanism to the other, on account of which the carbon fibers are subjected to buckling and disturbance in the orientation due to pulsing motion of the grasping mechanism, the both constituting the cause for hindrance in shaping the high performance carbon-fiber-reinforced plastic.
Incidentally, as the method for shaping such high performance carbon-fiber-reinforced plastic, in which more attention is paid to the strength sustaining factor (ROM %), there is a batch shaping method which combines the filament winding and the autoclave curing. This method, however, is considerably inferior in its productivity for the large-scaled space structure, hence it cannot be adopted for the purpose of the present invention.